In recent years, a magnetic head for perpendicular magnetic recording has been suggested to realize high recording density, large capacity or miniaturization of a magnetic disk device as a disk device. In this type of magnetic head, a recording head includes a main magnetic pole which produces a perpendicular magnetic field, a write shield magnetic pole provided on the trailing side of the main magnetic pole across an intervening write gap, and a coil for supplying a magnetic flux to the main magnetic pole. Further, there is suggested a high-frequency-assisted head wherein a high-frequency oscillator such as a spin-torque oscillator is provided in the write gap between the write shield magnetic pole and the main magnetic pole. Current is supplied to the spin-torque oscillator through the main magnetic pole and the write shield magnetic pole.
In the high-frequency-assisted head, a spin injection layer and an oscillation layer of the high-frequency oscillator are allocated in the write gap. In the high-frequency-assisted head having such a structure, a phenomenon (spin wave) in which the magnetization near the surface of the write shield or main magnetic pole facing the surface of the oscillation layer fluctuates synchronously with magnetization rotation in the oscillation layer occurs. There is a possibility that the spin wave disturbs magnetization rotation of the high-frequency oscillator and reduces the assist effect.